Method and system for providing inorganic vapor surface treatment for photoresist adhesion promotion

ABSTRACT

A system and method for forming a plurality of structures in a low dielectric constant layer is disclosed. The low dielectric constant layer is disposed on a semiconductor. The method and system include exposing the low dielectric constant layer to an agent that improves adhesion of a photoresist, providing a layer of the photoresist on the low dielectric constant layer, patterning the photoresist, and etching the low dielectric constant layer to form the plurality of structures.

The present application is a divisional of U.S. Ser. No. 08/980,888filed Dec. 1, 1997 now U.S. Pat. No. 6,066,578.

FIELD OF THE INVENTION

The present invention relates to semiconductor processing and moreparticularly to a method and system for transferring a photoresistpattern having reduced footing to low dielectric constant materials.

BACKGROUND OF THE INVENTION

Semiconductor technology has been increasing driven to lower devicesize. The feature size in the current conventional semiconductor devicesis on the order of 0.18 microns or less. As the size of featuresdecreases, the thicknesses of and separation between metal lines alsodecreases. However, the metal lines must still be insulated from eachother. As the separation between metal lines has decreased, conventionalhigh dielectric constant materials have become less desirable for use inisolating metal lines. Instead, low dielectric constant materials, suchas hydrogen silsequioxane (“HSQ”), are increasingly of interest forelectrically isolating structures in sub-0.25 micron technology.Generally, a material is considered a low dielectric constant materialwhen it has a dielectric constant on the order of 2.5 or below.

In order to use low dielectric constant materials to separate metallines, the low dielectric constant materials must be patterned andetched. The low dielectric constant material is first deposited on thesemiconductor. In a conventional method for semiconductor processing, aprimer would then be applied and photoresist would be spun on to the lowdielectric constant material. The photoresist would then be patterned.Finally, the low dielectric constant material would be etched to formstructures, such as trenches.

The adhesion of the photoresist to the low dielectric constant materialis not uniform. Instead, areas which do not adhere to the low dielectricconstant material are formed. When the photoresist is patterned, piecesof the photoresist which do not adhere to the low dielectric constantmaterial may break off. Moreover, when the low dielectric constantmaterial is etched, the areas etched may be the wrong size. For example,although trenches may be formed in the low dielectric constant material,conventional methods may not be able to form trenches of the appropriatesize, form, or separation.

In addition, the use conventional semiconductor processing methods whenprocessing low dielectric constant materials may result in resistfooting. Footing occurs when the photoresist that remains afterdevelopment does not have substantially vertical walls. Instead, a footis formed at the bottom of the wall of the feature. Thus, when the lowdielectric constant material is etched, the appropriate structure is nottransferred from the photoresist to the low dielectric constant materialbecause of the foot at the base of the remaining photoresist.

Accordingly, what is needed is a system and method for providing aphotoresist pattern having reduced footing and more accuratelytransferring the photoresist pattern to low dielectric constantmaterials. The present invention addresses such a need.

SUMMARY OF THE INVENTION

The present invention provides a method and system for forming aplurality of structures in a low dielectric constant layer. The lowdielectric constant layer is disposed on a semiconductor. The method andsystem comprise exposing the low dielectric constant layer to an agentthat improves adhesion of a photoresist, providing a layer of thephotoresist on the low dielectric constant layer, patterning thephotoresist, and etching the low dielectric constant layer to form theplurality of structures.

According to the system and method disclosed herein, the presentinvention provides a photoresist pattern having reduced footing andallows low dielectric constant materials to be more accuratelypatterned.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart of a conventional method used in conjunction withprocessing of low dielectric constant materials.

FIG. 2 is a is a block diagram depicting the semiconductor afterphotoresist is spun on using conventional processing methods.

FIG. 3 is a block diagram of a side view of a portion of thesemiconductor after the photoresist has been patterned.

FIG. 4 is a flow chart depicting a method for processing low dielectricconstant materials in accordance with the present invention.

FIG. 5 is a block diagram depicting the semiconductor after photoresistis spun on in accordance with the present invention.

FIG. 6 depicts a block diagram of a side view of a portion of thesemiconductor after the photoresist has been patterned in accordancewith the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to an improvement in processing of lowdielectric constant materials. The following description is presented toenable one of ordinary skill in the art to make and use the inventionand is provided in the context of a patent application and itsrequirements. Various modifications to the preferred embodiment will bereadily apparent to those skilled in the art and the generic principlesherein may be applied to other embodiments. Thus, the present inventionis not intended to be limited to the embodiment shown but is to beaccorded the widest scope consistent with the principles and featuresdescribed herein.

FIG. 1 is a flow chart of a conventional method for processingsemiconductors using low dielectric constant materials. The lowdielectric material is deposited via step 16. The low dielectricmaterial can be deposited by spinning it on the semiconductor or bychemical vapor (CVD) deposition. The low dielectric material may also bebaked. Typically, the low dielectric constant material has a dielectricconstant of approximately 2.5 or less. The photoresist is then appliedvia step 14. The step of providing the photoresist typically includesapplication of a primer followed by spinning on the photoresist. Oneconventional chemical primer used is hexamethyldisilazane (HMDS). Thechemical primer is supposed to improve the adhesion of the photoresistto the surface of the underlying low dielectric constant material. Thephotoresist is patterned via step 16. The low dielectric constantmaterial is then etched via step 16. Thus, structures such as trenchesare formed in the low dielectric constant material.

Although the structures in the low dielectric constant material formedusing the method 10 of FIG. 1 allow for smaller feature sizes, thosewith ordinary skill in the art will realize that the method 100 mayresult in structures which do not have the correct size and shape.

FIG. 2 depicts the system 20 after the spin on of the photoresist instep 14 of FIG. 1. The system 20 includes the semiconductor 22, a layerof low dielectric constant material 24, and a layer of photoresist 26.The semiconductor 22 is typically silicon. The low dielectric materiallayer 24 may be hydrogen silsequioxane (“HSQ”). Because the adhesion ofthe photoresist 26 to the low dielectric constant material 24 isnonuniform, there are bubble-like sections 28, 30, and 32 which do notadhere to the low dielectric constant material 24. The failure ofsection 28 to adhere to the low dielectric constant material 24 isindicated by the dark line 33 at the interface between the lowdielectric constant material 24 and the photoresist 26. The dark line 33represents a separation between the low dielectric constant material 24and the photoresist 26.

Because sections 28, 30, and 32 do not adhere to the low dielectricconstant material, one of ordinary skill in the art will recognize thatportions of sections 28, 30, and 32 may break off prior to etching ofthe low dielectric constant layer 24. In addition, one of ordinary skiffin the art will readily realize that structures formed in and aroundsections 28, 30, and 32 during etching of the low dielectric constantlayer 24 may not have the correct size because of the failure of thephotoresist 26 to adhere to the low dielectric constant material 24.

One of ordinary skill in the art will also realize that the conventionalmethod 10 of forming structures in the low dielectric constant material24 may result in resist footing. FIG. 3 depicts a portion of the system20 after step 16, patterning the photoresist. The remaining photoresist26 is shown on top of the low dielectric constant material 24. The lowdielectric constant material is disposed on the semiconductor 22. Thesidewalls 40 and 42 of the remaining photoresist 26 are notsubstantially vertical. Instead, the lower portion of each sidewall 40and 42 includes a foot. One of ordinary skill in the art will realizethat any structures etched into the low dielectric constant layer 24will not be of the correct size because the sidewalls 40 and 42 exhibitfooting.

The present invention provides for a method and system for generating aphotoresist pattern having reduced footing and more accuratelytransferring the photoresist pattern to a low dielectric constantmaterial. The present invention includes exposing the low dielectricconstant material to an agent that improves photoresist adhesion,providing photoresist on the low dielectric constant material,patterning the photoresist, and etching the low dielectric constantmaterial.

The present invention will be described in terms of the low dielectricconstant material HSQ and the use of a particular oxidizing gas.However, one of ordinary skill in the art will readily recognize thatthis method and system will operate effectively for other types of lowdielectric constant materials and other chemical agents which improvephotoresist adhesion.

To more particularly illustrate the system and method in accordance withthe present invention, refer now to FIG. 4 depicting a flow chart of amethod 100 for processing a semiconductor including a low dielectricconstant layer in accordance with the present invention. The method 100deposits the low dielectric constant layer via step 110. The lowdielectric constant material can be deposited using conventional methodsincluding spin-on and chemical vapor deposition. In a preferredembodiment, the low dielectric constant material is HSQ.

The semiconductor including the HSQ layer is then placed in an agentwhich improves photoresist adhesion, via step 112. In one embodiment,this agent is an oxidizing agent. In a preferred embodiment, theoxidizing agent is sulfur trioxide (SO₃) gas. In the preferredembodiment, the semiconductor is placed in a chamber. The chamber isthen evacuated and backfilled with sulfur trioxide gas. Also in apreferred embodiment, the flow of sulfur trioxide is regulated. However,nothing in the method and system prevents the regulation of sulfurtrioxide pressure rather than sulfur trioxide flow.

While in the sulfur trioxide, the semiconductor and low dielectric layermay also be heated. In a preferred embodiment, the semiconductor isheated to a relatively low temperature, approximately one hundreddegrees Centigrade. Preferably, the semiconductor is heated only tomoderately low temperatures, in the range of fifty to two hundreddegrees Centigrade. These low temperatures are preferred because the HSQdegrades if heated to higher temperatures.

In the preferred embodiment, the semiconductor is only placed in thesulfur trioxide for a relatively short time, often as few as 120 secondsor less. This is because sulfur trioxide is a relatively strongoxidizing agent. However, nothing prevents the exposure for a differenttime as long as adhesion of the photoresist is improved.

In one embodiment, once the semiconductor is removed from the oxidizingagent, it is washed and dried. A layer of photoresist is then providedvia step 114. In a preferred embodiment, providing the layer ofphotoresist includes the steps of applying a primer to the HSQ layerthen spinning on the photoresist. In a preferred embodiment, the primeris HMDS and is applied as a vapor. The photoresist can then be patternedand the HSQ layer etched via steps 116 and 118, respectively.

FIG. 5 depicts the system 120 after the photoresist has been spun on instep 14 of the method 100 in accordance with the present invention. Thesystem includes a semiconductor 122, a layer of HSQ 124, and a layer ofphotoresist 126. Because the semiconductor 122 and HSQ 124 were placedin sulfur trioxide, the adhesion of the photoresist 126 is uniform.Thus, there are no bubble-like sections 28, 30, and 32 of FIG. 2 whichmay be present when conventional processing methods are used.

Referring now to FIG. 6, a portion of the system 120 is depicted afterpatterning of the photoresist in step 116. The system 120 still includesthe semiconductor 22, the low dielectric constant layer 124, and theremaining photoresist 126. The remaining photoresist 126 has walls 140and 142. The walls 140 and 142 exhibit little or no footing.

Because the adhesion of the photoresist layer 126 is good and becausethe walls 140 and 142 of photoresist 126 remaining after patterningexhibit little footing, accuracy of the etching of the HSQ layer 124 isimproved.

Although the reason why adhesion of the photoresist layer 26 formedusing conventional processing method 10 is not completely known, it ishypothesized that chemical bonding of components of the low dielectricconstant layer 24 somehow prevents adhesion of the photoresist layer 26despite application of the primer. For example, it is postulated thatthe hydrogen in HSQ prevents the primer from bonding with the surface ofthe HSQ or allows only weak O—H bonds to be formed between the primerand the HSQ surface. As a result, the photoresist 26 does not adherewell to the surface of the low dielectric constant layer 24.

Placing the system 120 in the oxidizing agent, via step 112, changes thesurface chemistry of the HSQ layer 124. It is believed that the sulfurtrioxide reacts with the surface of the HSQ layer 124, oxidizing axialSi—H bonds and perhaps forming an O—H bonds. This, in turn, permits theprimer to bind to the treated surface of the HSQ layer 124 better. It ispostulated that the primer is able to form Si—Si bonds or Si—O bondsafter system 120 is placed in the oxidizing agent. The net result is theenhancement of photoresist 126 adhesion, which is spun onto the primedsurface of the HSQ layer 124. It is noted that high temperature methodsof treating the surface of the HSQ layer 124 are not used because theHSQ layer 124 degrades at high temperatures. Treatment with the sulfurtrioxide also decreases footing on the side walls 140 and 142, perhapsdue to reactions with between the sulfur trioxide and nitrogen existingin the HSQ layer 124 due to processing the HSQ layer in a gas containingnitrogen.

A method and system has been disclosed for treating a layer of lowdielectric constant material to improve photoresist adhesion and,therefore, improve accuracy of etching the photoresist layer. Althoughthe present invention has been described in accordance with theembodiments shown, one of ordinary skill in the art will readilyrecognize that there could be variations to the embodiments and thosevariations would be within the spirit and scope of the presentinvention. Accordingly, many modifications may be made by one ofordinary skill in the art without departing from the spirit and scope ofthe appended claims.

What is claimed is:
 1. A semiconductor device comprising: a lowdielectric constant layer having a plurality of structures formedtherein, the low dielectric constant layer having a dielectric constantof 2.5 or less, at least a portion of the plurality of structures beingformed by exposing the low dielectric constant layer to an agent thatimproves adhesion of a photoresist, the agent being an oxidizing agent,providing a layer of the photoresist on the low dielectric constantlayer, patterning the layer of photoresist to a desired size for each ofthe portion of the plurality of structures, and etching the lowdielectric constant layer to form the plurality of structures in the lowdielectric constant layer, the plurality of structures having thedesired size.
 2. The semiconductor device of claim 1 wherein the lowdielectric constant layer further includes hydrogen silsequioxane. 3.The semiconductor device of claim 1 wherein the agent is sulfur trioxidegas.
 4. The semiconductor device of claim 1 wherein the at least theportion of the plurality of structures are further formed by heating thelow dielectric constant layer to a moderately low temperature duringexposure to the agent that improves adhesion of the photoresist.
 5. Thesemiconductor device of claim 4 wherein the moderately low temperaturefurther includes temperatures below 200 degrees Centigrade.
 6. Thesemiconductor device of claim 4 wherein the moderately low temperaturefurther includes temperatures below 100 degrees Centigrade.
 7. Thesemiconductor device of claim 1 wherein the at least the portion of theplurality of structures are formed by exposing the low dielectricconstant layer to an agent that reduces footing.
 8. The semiconductordevice of claim 7 wherein the agent that reduces footing is the same asthe agent that improves adhesion of the photoresist.
 9. A semiconductordevice during fabrication comprising: a low dielectric constant layer,the low dielectric constant layer having a dielectric constant of 2.5 orless; and a photoresist layer on the low dielectric constant layer, thephotoresist layer having a plurality of apertures therein for forming aplurality of structures in the low dielectric constant layer, theplurality of apertures being formed by exposing the low dielectricconstant layer to an agent that improves adhesion of the photoresistlayer, the agent being an oxidizing agent, providing the photoresistlayer on the low dielectric constant layer, and patterning thephotoresist layer, such that a remaining portion of the photoresistlayer adheres to the dielectric constant layer and the plurality ofapertures are substantially free of footings.